Super cooler for a heat producing device

ABSTRACT

A super cooler device including a thermo electric cooler on a digital micro mirror device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/794,258, filed Mar. 4, 2004, which is a continuation of U.S.application Ser. No. 10/375,165, filed Feb. 25, 2003, now U.S. Pat. No.6,775,991, which is a continuation of U.S. application Ser. No.10/128,774, filed Apr. 22, 2002, now U.S. Pat. No. 6,523,353, which is adivisional of U.S. application Ser. No. 09/780,025, filed Feb. 9, 2001,now U.S. Pat. No. 6,430,934, which claims the benefit of U.S.provisional application Ser. No. 60/181,530 filed Feb. 10, 2000.

SUMMARY

The present application relates to cooling of a heat producing device,using a thermoelectric cooler arranged as a super cooler. Morespecifically, the present application teaches cooling of a device, suchas a digital mirror device, which requires a specified temperaturegradient across the device, using a supercooled element.

BACKGROUND

Electronic devices often have specified cooling requirements. One devicethat has specific cooling requirements is a digital micromirror device(“DMD”) available from Texas Instruments (“TI”). The manufacturer ofthis device has specified a maximum overall temperature for the deviceand also a specified maximum temperature gradient between the front andrear faces of the device during operation.

For example, the temperature of the specific DMD used in thisapplication needs to be kept below 55□ C, however, in this applicationit is desirable to keep the device at or below ambient. This may allowoperation in an ambient environment up to 55□ C, such as may beencountered in a stage theater or studio environment. The temperaturedifferential between the front and rear of the DMD cannot exceed 15□.Besides the heat from the operation of the DMD itself, large amounts ofheat from a high intensity light source must be dissipated.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects will now be described in detail with referenceto the accompanying, wherein:

FIG. 1 shows an exploded diagram of the parts making up the supercoolerassembly;

FIG. 2 shows the rear of the DMD and parts which are assembled to theDMD;

FIG. 3 shows a circuit for driving a thermoelectric cooler; and

FIG. 4 shows a flowchart of operation.

DETAILED DESCRIPTION

According to the present system, a “supercooler” device, is used tomonitor and control the temperature of a device which can control lighton a pixel-by-pixel basis, e.g. a digital mirror device (DMD).

The mechanical structure of the supercooling assembly is shown inFIG. 1. The pixel element is a DMD 99, which forms part of a DMDassembly 100. As shown, a thermal connection 105 to the DMD 99 isprovided. A lighting projector 155 projects light 156 on the frontsurface 157 thereof.

A cold plate 120 is assembled to a mounting bracket 110 in a mannerwhich allows minimal thermal transfer between the two components. TheDMD is attached directly to the cold plate 120, hereby allowing maximumthermal transfer between the DMD and cold plate 120, but minimal thermaltransfer to the mounting bracket 110. The rear surface of the cold plate120 is directly connected to one side of the thermoelectric device 130,and the other side of the thermoelectric device is connected to a heatsink/fan assembly 140.

Insulating foam gaskets are fitted around the DMD rear stud, the coldplate, and the thermoelectric device in order to isolate them from theoutside ambient air. This improves the efficiency of the cooling systemby eliminating the effects of condensation and properly controlling theflow of heat from the DMD to the cold plate, through the thermoelectricdevice, and into the heat sink/fan assembly.

The thermoelectric cooler element 130 operates as conventional toproduce one cold side 131 and one hot side 132. The hot side is coupledto the heat sink/fan assembly 140 to dissipate the heat. In a preferredmode, the heat sink/fan assembly is columnar is shape, with asubstantially square cross section. This facilitates using a squareshaped fan housing 142. The square shaped fan unit allows the maximumuse of the space for a fan, whose blades usually follow a round shape.Any type of cooling fan, however can be used.

The DMD assembly 100 has an extending rear stud 105 which is coveredwith thermal grease. This stud extends though a hole 112 in the bracketassembly 110.

The plate 120 is actively cooled, and hence becomes a “cold plate”. Theactive cooling keeps the metal plate at a cooled temperature, and thethermal characteristics of the plate material allow the heat flowinginto the plate from the DMD to be evenly distributed throughout theentire plate. The plate is preferably about ¼″ to ⅜″ in thickness, andof comparable outer size to the thermal contact area of thethermoelectric cooler element 130. This allows the localized andconcentrated heat at the rear stud of the DMD to be evenly dissipatedthrough the cold plate and then efficiently transferred through the fullsurface area of the thermoelectric cooler element. As shown, theassembly employs thermal insulation techniques such as fiber/plasticsleeves and washers in the mounting of components, in order to preventheat transfer via mounting screws etc. Since this heat transfer could beuncontrolled, it could otherwise reduce the cooling efficiency.

The front of the DMD is shown in FIG. 2. Temperature sensor 200 ismounted to have a fast response to temperature changes. A secondtemperature sensor 122 is mounted to the cold plate 120 and effectivelymeasures the temperature of the rear of the DMD 99. This secondtemperature sensor 122 therefore monitors the back temperature.

The hot side 132 of the thermoelectric cooler is coupled to a heat sinkassembly 130. The heat sink assembly 140 includes a heat sink element140. As shown, the device has fins and a top-located cooling fan 142.

A block diagram of the control system is shown in FIG. 3. Controller 300operates in a closed loop mode to maintain a desired temperaturedifferential across the sensors 122,200.

One important feature of the present application is that thethermoelectric cooler is controlled to maintain the temperature of theDMD at the desired limits. These limits are set at a target of 16□ C onthe front, and a differential no greater than 15□ between front andrear. The thermoelectric cooler is controlled using very low frequencyor filtered pulse width modulation. In a first embodiment, thecontrolling micro controller 300 produces an output 302, e.g., digitalor analog. This drives a pulse width modulator 304. The output of thepulse width modulator is a square wave 306 or a signal close to a squarewave, with sufficient amplitude and power to produce the desired levelof cooling down the thermoelectric cooler. The square wave is coupled toan LC filter 308 which has a time constant effective to smooth the 20KHz switching frequency. The output to the thermoelectric cooler istherefore a DC signal. This drives the thermoelectric cooler 130 andcauses it to produce a cooling output. In a second embodiment, the LCfilter is removed and the TEC is driven directly by the square wave 306at a lower frequency, e.g. 1 Hz.

The microcontroller operates according to the flowchart of FIG. 4. Step400 determines if the temperature of the first temperature sensor T1 isgreater than 16□. If so, the output to the TEC remains “on”, resultingin further cooling. When the temperature falls below 16□, the drive tothe TEC is switched off. The sample period is approximately ½ secondbetween samples.

At 410, the system checks temperature of the first sensor (T1) and ofthe second sensor (T2) to determine if the differential is greater than15□. If so, the output is switched “on”. Step 420 indicates a limitalarm, which represents the time of increase if the rate of changecontinues. If the rate of change continues to increase, as detected atstep 420, a fault is declared at step 425. This fault can cause, forexample, the entire unit to be shut off, to reduce the power and preventpermanent damage.

Other embodiments are contemplated.

1. A system, comprising: an electrically controllable device that iselectrically controllable to control light on a pixel by pixel basis;and a cooling device, connected thermally to said electricallycontrollable device, and operating to actively cool said electricallycontrollable device, where said operating provides a first nonzeroamount of cooling based on detecting a need for providing a firstcooling amount, and where said operating provides a second nonzeroamount of cooling, based on detecting a need for providing a secondnonzero cooling amount, wherein said first nonzero cooling amount isdifferent then said second nonzero cooling amount.
 2. A system as inclaim 1, wherein said need for a cooling amount depends on a temperaturedifferential between a front surface and back surface of saidelectrically controllable device.
 3. A system as in claim 1, whereinsaid electrically controllable device is a digital mirror device.
 4. Asystem as in claim 1, wherein said cooling device carries out said firstcooling amount and said second cooling amount using pulse widthmodulation of an electrically controllable cooling device.
 5. A systemas in claim 1, wherein said cooling device turns on for a first time andturns off for a second time to change said amount of cooling.
 6. Asystem as in claim 1, wherein said electrically controllable device isthermally connected to a thermally conducting plate, and said coolingdevice is thermally coupled to said thermally conducting plate.
 7. Adevice as in claim 6, wherein a portion of said thermally conductingplate extends through said plate.
 8. A device as in claim 1, whereinsaid cooling device includes a thermoelectric cooler.
 9. A system,comprising: an electrically controllable device that is electricallycontrollable to control light on a pixel by pixel basis; a coolingdevice, thermally coupled to said electrically controllable device, andcooling said electrically controllable device; and a controller for saidcooling device, controlling said cooling device based on a temperaturedifferential between a front surface of said electrically controllabledevice and a rear surface of said electronically controllable device.10. A system as in claim 9, wherein said controller includes atemperature sensor on a front surface of said electrically controllabledevice and a temperature sensor on a rear surface of said electricallycontrollable device.
 11. A system as in claim 9, wherein said controllercontrols an amount of cooling per unit time between multiple coolingnonzero values.
 12. A system as in claim 11, wherein said amount ofcooling per unit time is carried out based on pulse width modulation.13. A system as in claim 11, wherein said cooling device includes athermoelectric cooler.
 14. A system as in claim 9, wherein saidelectrically controllable device is attached to a thermally conductiveplate, and wherein said cooling device is connected to said plate andnot to said device.
 15. A method, comprising: operating an electricallycontrollable device that is electrically controllable to control lighton a pixel by pixel basis, said operating comprising changing an appliedlight beam to create a light output; cooling said electricallycontrollable device, and cooling said electrically controllable device;and controlling an amount of a cooling device that is used to cool saidelectrically controllable device, based on a temperature differentialbetween a front surface of said electrically controllable device and arear surface of said electronically controllable device.
 16. A method asin claim 15, wherein said controlling comprises controlling an amount ofcooling per unit time between multiple nonzero cooling values.
 17. Amethod as in claim 16, wherein said amount of cooling per unit time iscarried out based on pulse width modulation.
 18. A method as in claim15, wherein said cooling uses a thermoelectric cooling.
 19. A method,comprising: operating an electrically controllable device that iselectrically controllable to control light on a pixel by pixel basis,said operating comprising changing an applied light beam to create alight output; and controlling cooling of said said electricallycontrollable device, wherein said controlling provides a first nonzeroamount of cooling based on detecting a need for providing a firstcooling amount, and where said operating provides a second nonzeroamount of cooling, based on detecting a need for providing a secondnonzero cooling amount, wherein said first nonzero cooling amount isdifferent then said second nonzero cooling amount.
 20. A method as inclaim 19, wherein said need for a cooling amount depends on atemperature differential between a front surface and back surface ofsaid electrically controllable device.
 21. A method as in claim 19,wherein said cooling turns on for a first time and turns off for asecond time to change said amount of cooling.
 22. A method as in claim19, wherein said electrically controllable device is thermally connectedto a thermally conducting plate, and said cooling device is thermallycoupled to said thermally conducting plate.